1. Field of the Invention
This invention relates to devices for supporting the foot of a human user and controlling the stresses applied thereto while the user is standing or in gait. In particular, the invention relates to orthopaedic orthotic devices for insertion into a shoe.
2. Description of Related Art
Most orthotic devices are designed to distribute the stresses of weightbearing to areas of the foot which can best tolerate such stresses, in order to maximize comfort and minimize trauma to the sole of the foot. Such an orthosis provides a padded surface which may be flat, or which may be shaped to conform with the contours of a particular foot (a custom molded orthosis) or an average foot (a non-custom orthosis). Non-custom accommodative orthoses tend to be either significantly flatter than the average sole, or to be fabricated from a soft material which compresses under loads of less than about 5% of body weight so as to be tolerated across a population possessing wide variations in sole contour. Such devices may increase foot comfort, but are unlikely to provide significant control of foot motion.
A corrective orthosis, on the other hand, is designed to guide and restrict the motion of joints of the foot in order to improve gait efficiency and to reduce the stresses imposed on lower extremity anatomical structures during gait. As a rule, corrective orthoses are fabricated of firmer materials than are devices intended simply to provide comfort to the foot. The main goal of most corrective orthoses is to resist pronation, a complex foot motion which produces the partial collapse of the medial longitudinal arch of the foot, best seen during the midstance phase of the gait cycle.
Pronation actually consists of the abduction, eversion, and dorsiflexion of the forefoot in relation to the rearfoot. Because of the close contiguity of the joints involved, pronation is always accompanied by eversion of the heel and internal rotation of the leg and hip. While pronation is a normal part of gait, it is now well established that excessive pronation is the source of many lower extremity pathologies, including muscle tiredness and inflammation, foot and knee joint pain, tendinitis, ligament strain, and even neurological damage. Excessive pronation also renders the gait less efficient since time and effort is wasted in collapsing (pronating) and recovering (supinating). It has been estimated that up to 70% of the population overpronates to some degree.
Peak forces transmitted through the feet during running can easily exceed three times body weight. In order to resist such forces, a functional orthosis must be fabricated of a firm material. To remain comfortable and to avoid painful high pressure spots, it must also conform closely to the contours of the sole of the foot in its neutral position. Proper arch height is particularly critical in a functional orthosis. If the arch is too high, the device will be intolerably painful. On the other hand, if the arch is too low, control of pronation will be sacrificed. Significantly, due to the high forces transmitted through feet during gait, small variations in the form and material of orthoses can produce profound differences in orthosis function and comfort.
To satisfy the dual requirements of firm support and precisely contoured fit, prior art corrective orthoses have generally ben produced from a custom mold of an individual foot. In addition to the disadvantages of the tedium and expense of the custom-molding procedure, such prescription devices frequently require modifications subsequent to fitting.
Further, currently available corrective orthoses are plagued by several additional shortcomings. First, these devices are typically bulky. To accommodate the orthosis, a shoe's insole, if present, must typically be removed or the shoe must be replaced with another of larger size. In either case, the fit of the shoe is altered. Moreover, insertion of such a device into the shoe raises the center of gravity of the foot within the shoe, thereby destablizing the foot. By changing the fit of the shoe, these devices frequently counteract the supportive design features of the shoe.
Another disadvantage shared by currently available corrective orthoses is that they are typically fabricated of rigid material, e.g., hard plastics. Prolonged wear of such rigid devices causes degradation of the foot's plantar fat pad, leading to the formation of painful calluses.
An example of a device which suffers from several of the deficiencies referred to above is shown in Friedlander, et al., U.S. Pat. No. 4,360,027. The device of Friedlander, et al. is apparently intended to control overpronation of the foot during gait. However, unlike the present invention, this function is achieved in part through placement of a "posting" material at supporting points in the Friedlander, et al. device (e.g., the longitudinal arch and heel supporting region). While supportive, posting is a hard, rigid material whose presence in the device requires that it be custom-fitted to avoid pain through exposure of the foot to posting at inappropriate sites (Friedlander, et al., Col. 4, lines 6-9).
The focus of the Friedlander, et al. device on the control of pronation led to the use of a medial, arch portion of the device which is somewhat thicker and wider than the portion of the device adjacent to the metatarsals of the subject's foot (Friedlander, et al., FIGS. 1 and 3). Although this design facilitates control of pronation, it may also cause additional strain to be placed on the metatarsals of the foot by shifting stress pressure from the middle portion of the foot forward without compensation for the additional strain on the metatarsals.
A need, therefore, exists for an orthotic device capable of addressing many of the etiologies of pain in the foot with minimal intrusion into, and deformation of, the internal space of the shoe in which the device is placed. The present invention meets this need.